In the operation of steam flooding to stimulate production of oil from oil reservoirs it is important to have a simple and accurate method to determine the quality and mass flow rate of steam at the well head of an injection well. In such a stimulation process the amount of heat input to the reservoir determines the rate and amount of oil recovery, and heat input depends directly upon the steam quality and mass flow rate. Steam that is generated for injection into the reservoir generally arrives at the well head as wet steam, i.e., a mixture of vapor and liquid, at super-atmospheric pressure. A given mass of dry steam, i.e. steam of 100% quality, has a higher heat content than the same mass of wet steam at the same temperature and pressure. The greater the steam quality and the the mass flow rate are, the more the heat input to the reservoir will be. Steam quality and mass flow rate thus directly affect the rate and the ultimate amount of recovery of oil, and therefore have a bearing upon earnings and investment requirements.
Heretofore, steam quality measurements of the steam in a line to an injection well have been made using throttling orifices, making various temperature, pressure, and flow measurements, and calculating the quality of the steam in the line. This necessitated the use of a substantial piece of equipment. However it has been found that when there are several separate lines coming off one distribution manifold, each line going to a different injection well, one cannot rely on the steam quality measured in the manifold to represent the quality in any of the separate lines to the wells. In the case of a manifold having T joints, for example, the steam that has turned a corner will have a higher quality than the steam that has continued moving in a straight line, all other things being equal, since the greater momentum of the liquid phase compared to the vapor phase will result in mechanical separation of the liquid and vapor components and a higher liquid content in the straight line component. Consequently, it has heretofore been impossible to know the quality in the separate lines to the different injection wells from one quality determination at the manifold and it has been impractical to make a quality determination on each separate line using a substantial piece of equipment for each such line.
It is therefore highly desirable to have a relatively simple method and apparatus to make separate steam quality and mass flow rate determinations on each of the individual lines to separate injection wells in order to know the rate of heat input to the reservoir through each separate injection well.